Polarized gas is defined as a gas in which the nuclear spins are preferentially aligned with an external magnetic field. These gases are used in a variety of scientific fields, most recently in MRI medical applications. The MRI application of the polarized gas requires a pressure in the one bar or higher range. One method of producing such a polarized gas is by metastability-exchange optical pumping of a helium gas. This can only be accomplished at pressures of a few millibar necessitating compression of the gas without too great a loss of polarization.
Prior compression techniques and apparatus used in the polarization of gases have either been extremely costly, or have caused the polarized gas to suffer a great loss in polarization. In addition to being costly, the apparatus heretofore have been bulky and complex. For example, R. Surkau at al. in Realization of a Broad Band Neutron Spin Filter with Compressed Gas, published in Nuclear Instruments and Methods in Physics Research A 384, (1997), a method and apparatus for the compression of a helium gas. This method requires the use of a piston compressor constructed of titanium in order to avoid depolarization of the helium gas during compression. Moreover, the apparatus as described because of the physical size of the components is several cubic meters in size.
The prior art discusses in a thesis by Thomas Prokscha, University of Mainz, Germany, October of 1991 the use of a diaphragm pump in the compression process but rejects the idea in that they were primarily built out of magnetic material such as high grade steel. The electric motor will produce an non-homogenous magnetic field, and the diaphragm pump tested was considered to be too permeable to the ambient atmosphere.
A recent example of polarization of noble gases is U.S. Pat. No. 5,642,625, issued to Cates, Jr. et. al, it discloses an apparatus for hyperpolarization of noble gases and storage techniques of the gases.
What is needed but not provided in the prior art is an improved method of polarization of a helium gas and an apparatus for the compression of the helium gas with a reasonably high preservation of the polarization of the gas. Additionally, it would also be helpful to provide such features in a compact, inexpensive, and simple design. Finally, it would be helpful to provide such a mechanism which facilitates compression of the gas to 1 bar or greater.